Table 26.7
Construction buffer distances for low magnitude impact
Construction Phase Landfall
Cable system installation
Horizontal Directional Drilling Converter stations construction
Noise buffer distance (m) 75 80 36
120
44. A distance propagation calculation was performed on each of the sound power levels listed in Table 26.6 to establish the point at which the 65dB LAeq 12hr impact level would be achieved for the different construction phases. Using a geographic information system (GIS) it was then possible to determine any areas where residential properties would be exposed to construction noise levels greater than the 65dB LAeq 12hr impact threshold level. As the 65dB LAeq 12hr threshold represents the change from negligible to low magnitude effect for normal daytime working, it follows that any receptors outside the buffer areas will experience a negligible effect.
Off-site construction traffic noise 45.
Off-site construction related traffic impacts were assessed by calculating the relative increase in road traffic flow on road links used by construction traffic.
46. Noise level increases due to increases in traffic volume on surrounding local roads were assessed in accordance with the methodology contained in Calculation of Road Traffic Noise (CRTN) and DMRB. The significance of any predicted change in noise level was then assessed in accordance with the criteria contained in DMRB.
47.
Following the methodology contained in DMRB (Volume 11, Section 3, Chapter 3) an initial screening assessment was undertaken to assess whether there were any significant changes in traffic volumes as a result of the development. Any road links with a predicted increase in traffic volume of 25%, or a decrease of 20%, were identified in the initial part of the assessment. Such changes in traffic volume would correspond to a 1dB(A) change in noise level over an 18 hour period on the relevant road link. A change in noise level of less than 1dB(A) is regarded as imperceptible and therefore negligible with regard to impact significance. If there is no increase greater than 25% or a decrease of 20% or greater, then the guidance indicates that no further assessment needs to be conducted (Highways Agency 2011).
48. Where road links were predicted to have an increase of greater than 25% or a decrease of 20%, a noise level calculation should be undertaken following the procedure outlined in CRTN. The baseline and baseline plus construction HGV flows
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 26 Noise and Vibration Page 15
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